The system for controlling the horizontal brush in the rollover units or tunnel washing systems, has the task of moving the same along the entire profile of the vehicle maintaining a determined travel velocity and regulating the contact between the bristles and the bodywork in the best way possible.
Regardless of the travel speed, in order to have the ideal performances the pressure exerted by the bristles onto the surface must be uniform on all the points of contact and for the entire length of the longitudinal profile of the vehicle.
For proper washing with a suitable contact and the minimum risk of damage, the pressure of the bristles on the bodywork must be comprised between fixed minimum and maximum values.
Therefore, all the known control systems are based on the direct or indirect reading of the contact pressure.
A serious drawback is encountered when the vehicle to be washed has such an irregular surface to hinder the control, at certain points, from obtaining an accurate calculation of this fundamental parameter.
It is known that the control systems based on reading the absorption of the brush rotation motor operate on the total force obtained from the sum of the forces applied on all the points of the contact surface.
Regarding the regular and smooth surfaces it can be argued that the absorption current is approximately proportional to the total contact area of the brush against the vehicle. This surface can be interpreted as a rectangle of the same width as the bodywork at the point of contact and of a length proportional to the plunge. Given that the control attempts maintain the absorption current constant while the brush follows the profile of the vehicle, what occurs is that the plunge is modified in a manner inversely proportional to the width of the of the contact surface at all points. In other words the smaller the width the greater the plunge and, vice versa, the greater the width the smaller the plunge.
This situation divides types of vehicles in two categories: safe vehicles with regular surfaces, usually vehicles with closed bodyworks and without projecting accessories, for which the variation of the width is restricted and the plunge difference obtained is usually tolerable; and potentially risky vehicles with an irregular surface, usually vehicles with parts of the bodywork open such as pick-ups with an open rear an/or with roll bars, vehicles with ski boxes or other boxes fixed on the roof, off-road vehicles with spare wheels, vehicles with particular thin projections such as lights etc, which require special solutions from time to time.
For example, there is a special solution for vehicles of the pick-up type which prevents the brush from lowering onto the rear part where, possibly, critical situations might occur. For cleaning cycles which start from the rear part during the first travel forward, the brush moves only upwards, that is once it reaches the maximum height it remains at that position up to the end of the vehicle, while during the second travel backwards the brush starts from a low position at the rear moving only upwards and once it reaches the point where it had left the surface in the previous pass, the downwards movement is enabled. On the contrary, if the washing cycle starts from the rear part of the vehicle during the first travel backwards, the brush starts at a low position at the rear moving only upwards and once it reaches a preset distance from the front of the vehicle, the downward movement is enabled.
The drawbacks of this type of control lie: first and foremost in the fact that it does not consider the projections on the front or on the roof of the vehicle, for example spare wheels on the bonnet, ski-boxes, lights etc; secondly, in the fact that some projecting parts such as bars on the rear part of the vehicle or the absence of the rear door of a pick-up might lead to damages on the vehicle or the blocking of the system due to emergency; thirdly in the fact that it does not have a universal use in that it cannot be used on the other vehicles (vehicles with a regular profile etc) given that, during the forward travel it would not wash the entire rear from the roof to the bumpers, and hence, there arises the need to identify the pick-ups before selecting the washing programme; and fourthly, in the fact that the pick-ups cannot be identified in an accurate manner through automatic means due to the danger of causing damage, thus the selection is performed manually by the client.